Here is a quick, inexpensive, and proven (to me) desiccant solution I have used for a couple years to help keep the tools in my shop and the ammo rust and moisture free. We are in Central Texas and the tools are in a non-climate controlled but insulated metal building. Details of that are HERE.
So far no rust on any tools and all my ammo looks good.
Here is what you need:
1 bag Silicone kitty litter
1 cup measuring cup
I pour the kitty litter into a plastic container for easier use. Then I measure 1 solid cup of kitty litter out and pour it into an empty paint strainer. There is some silicone dust that I shack out through the strainer and then zip strip the top closed. I then add 1 strainer per ammo can and 1 strainer per tool drawer.
Here is a shot of what I use and what the strainers look like when I am done:
Here is a picture of old/used desiccant vs. new. New is the brighter stuff in the cup:
More Images HERE